Wildfire‐Specific PM _2.5 Asthma Risk Across a Disproportionately Burdened Pediatric Population in Northern California

Wildfire smoke events have increased in severity and impact over the past two decades and are expected to remain a major contributor to air pollution especially in the Western U.S. Children and communities with pre-existing environmental and socioeconomic disadvantages, such as those in Alameda and Contra Costa Counties, which rank among the highest in California for asthma-related health burdens, face disproportionate risks from these events. In this retrospective study, the association between wildfire-specific PM_2.5 exposure and asthma-related hospital encounters was evaluated among children (0-18 years old) in these two counties from January 2017 to February 2020 at a regional children's hospital. Distributed lag quasi-Poisson regression models were used to assess short-term impacts up to six days post-exposure. Over 9,300 hospital visits were modeled and found that wildfire-specific PM_2.5 was associated with increasing asthma-related hospital encounters. Specifically, each 10 μg m^-3 increase in wildfire-specific PM_2.5 was associated with a 4% (95% CI: 0%-8%) increase in pediatric hospital encounter risk on the day of exposure, with additional 3%-4% increases on days 3 and 4 (95% CI: 1%-4% and 1%-6%, respectively). Cumulatively, these exposures corresponded to a 13% (95% CI: 9%-18%) increased risk over the five-day lag period. Baseline hospital encounter risk varied across census tracts, reflecting underlying community vulnerabilities. Notably, wildfire-related health risks were amplified in communities with high baseline vulnerability compared to communities with lower vulnerabilities. These findings quantify the risk of wildfire smoke in communities already facing environmental and socioeconomic disadvantages, emphasizing the need for targeted public health interventions in high-risk areas.